Commutator design



Patented Dec. 2, 1947 COM'MUTATOR DESIGN Louis H. Inman, Tulsa, Okla, assignor to Well Surveys, Incorporated, Tulsa, Okla, a corporation of Delaware Application April 26, 1945, Serial No. 590,479

6 Claims.

This invention relates to the art of well surveying and more particularly to a specific part of the apparatus used in conduct ng well surveys, namely, the capacitative commutator.

In the radioactivity method of well surveying, electrical signals are generated by an electrometer in the bore hole that are proportionally related to the detected radioactivity of the strata adjacent the bore hole, and these signals are transmitted to the surface where they are recorded in coordination with the depths at which they were generated. Originally, when using an ionization chamber as a detecting means the voltage developed across the res stance, which was connected in the electrode circuit of the ionization chamber, was used directly to govern an ampl fier which amplified thesignals and transmitted them to the surface for recording. This method, however, was subject to the objection that direct current amplifiers are subject to drift and produce such inaccuracies in the record that they prove to be impractical.

In order to overcome this objectionable feature of the original method of conducting surveys it was found desirable to commutate the varying direct current signal of the ionization chamber circuit and use the commutated signal for the operation of an alternating current amplifier, which sent its signals to the surface of the earth where they were demodulated and recorded as continuous current signals that varied in amplitude accordance with the variation of the radioactivity detected.

Although improvements on this system which comprised the inauguration of a null system for recording the signals generated by the detecting instrument have effected a marked improvement in the results obtained. the capac tative commutator is still an essential element of the apparatus.

These capacitative commutators are usually in the form of a variable condenser having one fixed or stator blade and a moving or flexor blade which may be in the form of a reed. The flexor b ade is driven at a definite controlled frequency. This frequency in some commercially successful apparatus has been selected as about '74 cycles per second. Driving means in the form of a. power source connected in series with a carbon button. and a solenoid are usually employed for the actuation of the reed.

Heretofore these carbon buttons have had one face firmly anchored to a su port and the other face ri idly fixed throu h a connecting link to the vibrating element so that the vibrating element .ing therethrough. Rigidly attaching one face of the button to the flexor blade of the capacitative commutator has proven to be destructive to the carbon button. Due to the fact that the force supplied to the face of this button is not directly in line with the axis of the button it tended to set up unnatural stresses in the faces of the button, which in a short time fatigued the material in the faces of the button, causing it to rupture,

Since these capacitative commutators are necessarily a part of the subsurface apparatus they are enclosed in a pressure-resisting capsule that is adapted to withstand the high pressure encountered in surveying deep wells. These capsules are assembled in the laboratory for field use with special equipment which is not readily available to field crews using the apparatus. Therefore, trouble occasioned by the fa lure of the car bon button which regulates the power for driving the capacitative commutator necessitates the return of the capsule to the laboratory, where it was assembled, for repair, resulting in a stoppage of the work by the entire field crew and the accompanying expense due to loss of time.

This invention is directed to an improvement of the means for attaching the carbon button to the flexor blade of the capacitative commutator and provides for the free movement of the fiexor blade without the introduction of spurious frequencies of vibration therein.

Additionally, this invention provides for the application of force to the carbon huttnn flew-tn,- in line with the axis of the button resulting in a natural stress being placed on the faces of the button which will result in a maximum life of the carbon button.

A complete understanding of the present invention can be had from the following detailed description when considered with the drawings in which,

Figure 1 is a schematic diagram showing the function of the carbon button in a well surveying apparatus;

Figure 2 is an enlarged elevation of the capacitative commutator showing the carbon button and the means by which it engages the flexor blade of the commutator; and

Figure 3 is a cross-sectional view of the capacitat ve commutator taken along the lines 33 of Figure 2.

Referring to the drawings in detail. particularly Figure 1, there is shown schematically the apparatus used in conducting a radioactivity well survey. That portion of the apparatus enclosed in the dashed line rectangle I is contained within a pressure resisting capsule and is adapted to be lowered into a drill hole. The ionization chamber ll, having the resistance l2 and the battery [3 connected in series with its electrodes, produces electrical signals that are in the form of continuous current signals that vary in amplitude in accordance with the intensity of the radiation entering the ionization chamber. The variation of the current flowing through the resistance l2 produces a voltage drcp that is impressed across the capacitative commut-tor Id. The capacitative commutator l4 being driven at a definite frequency, by means not shown in this figure, converts the continuous current into a pulsating current at the frequency at which the fleXor blade of the commutator is driven. The pulsating current thus produced is impressed on the alternating current amplifier l5 through coupling condenser IE. The amplified signals are then impressed on the cable H and the ground l8. The recording circuit comprises the cable II, the recorder I9, the conductor 20 and return circuit through ground to conductor '8. In order that the signals when recorded will be in correlation with the depth at which they were generated in, the cable I! is caused to pass over a measuring wheel 2| which is synchrnized with the driving mears for the recorder I9 or the take-up paper roll of the recorder.

Referring to Fi ure 2 the capacitative commutator Hi comprises a heavy housing 22 which is firmly anchored by appropriate means to the inner wall of the capsule which houses the subsurface equipment. The support is necessarily made heavy in order to eliminate spurious frequencies which would be developed by the vibration of the flexor blade, since the flexor blade is anchored to one end of the housing by means of the screw 23. The flexor blade 24 passes through the housing 22 and out through a slit 25 provided therein. The free end of the fiexor blade extends through the slit far enough to present the desired surface to a fixed stator blade 28 which is likewise anchored to the inner wall of the capsule, or to framework carried thereby, by appropriate means not shown. Disposed within the housing 22 is a carbon button 27 of conventional design. Face 28 of the carbon button 21 is anchored to the housing 22 by means of the link 23 and the screw 36. The opposite face of the carbon button, face 35, is connected by means of the screw 32 to a U-shaped link 33 which carries at its free end novel means 34 for engaging the flexor blade. The novel means by which face 3| of the carbon button is secured to the flexor blade comprise a U-shaped phosphor bronze spring that is secured to the free end of link 33 in such a manner that the arms of the U-shaped phosphor bronze spring straddles the flexor blade. The phosphor bronze spring is secured to the link 33 by one of its arms at 35, as clearly shown in Figure 3. The arms of the U-shaped phosphor bronze spring do not contact the fiexor blades but are provided with hemispherical buttons 36 which are attached to the inner surfaces of the ends of the arms of the U-shaped spring. These hemispherical buttons may be formed of some hard material, such as synthane, which has temperature characteristics that are desirable for this particular type of apparatus. These hemispherical buttons 36 make positive contact with opposite sides of the fiexor blade thereby securing the carbon button to the flexor blade. In this manner point contact is made with the blade whereas by the old method a substantial portion of the surface of the blade was engaged by clamping surfaces. The fiexor blade is allowed free movement in driving the carbon button, and, therefore, will not have unnatural frequencies produced in it which were due to stresses set up by the old form of clamp.

In operation, a source of power, such as the battery 31, is connected in series with the solenoid 38 and the carbon button 2?. Due to the arrangement of the solenoid winding, completion of a circuit through the battery, solenoid and carbon button, will cause the fleXor blade to be stressed away from the stator blade 25. This action decreases the packing of the carbon granules in the carbon button 21, thereby presenting a greater resistance to the flow of current in the series circuit. Due to the reduction of the current through the solenoid 38 the plate will swing back of its own accord toward the stator blade, thereby packing the carbon granules in the carbon button 21 and decreasing the resistance that it presents to the series circuit. This will allow the current to increase through the solenoid and again draw the fieXOr blade away from the stator blade 26. This cycle will be repeated over and over again and its frequency will be controlled by the natural frequency of the fiexor blade.

Although this invention has been specifically described in connection with well surveying apparatus, it is obvious to those skilled in the art that this novel means of linkage between a carbon button and a fiexor blade that it is adapted to drive, has broad application and the present invention is to be limited only by the scope of the claims appended hereto.

I claim:

1. A capacitative commutator comprising in combination a stationary element, a driven element, means for driving said driven element, means for controlling said driving means and means for connecting the controlling means to the driven element, said connecting means comprising a resilient member connected at one end thereof to said controlling means, means carried by the opposite end of said resilient member for making point contact with opposite sides of the driven element.

2. A capacitative commutator comprising in combination a stationary element, a driven element, means for driving said driven element, means for controlling said driving means and means for connecting the controlling means to the driven element, said connecting means comprising a link connected at one end thereof to said controlling means, means carried by the opposite end of said link for making continuous point contact with the driven element.

3. A capacitative commutator comprising in combination a stationary element, a driven element, means for driving said driven element, a carbon button for controlling said driving means and means for connecting the carbon button to the driven element, said connecting means comprising a resilient member connected at one end thereof to said carbon button, means carried by the opposite end of said resilient member for making point contact with opposite sides of the driven element.

4. A capacitative commutator comprising in combination a stationary element, a driven element, means for driving said driven element, a

carbon button for controlling said driving means and means for connecting the carbon button to the driven element, said connecting means comprising a link connected at one end thereof to said carbon button, means carried by the opposite end of said link for making continuous point contact with the driven element.

5. A capacitative commutator comprising in combination a stationary element, a driven element, means for driving said driven element, a carbon button for controlling said driving means and means for connecting the carbon button to the driven element, said connecting means comprising a. link connected at one end thereof to said carbon button, means carried by the opposite end of said link for making continuous point contact with opposite sides of the driven element.

6. In a. capacitative commutator having a stationary element, a. driven element, means for driving said driven element, and means actuated by said driven element for controlling said driving means, the improvement which comprises resilient means connecting the driven element to said controlling means, and means carried by said resilient means for making point contact with opposite sides of the driven element.

LOUIS H. INMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain of 1884 

